The overall goal of this proposal is to test the hypothesis that adenosine, a purine nucleoside and potent vasodilator, is involved in cerebral blood flow (CBF) regulation. Our previous studies (years 01-03) characterized the changes in whole brain adenosine concentrations in ischemia, hypoxia, hypotension and seizures. More recently (years 04-07.5), we established a causal relationship between adenosine and CBF. In the present proposal, we plan to utilize a multidisciplinary approach to dissect the component elements of the microcirculation affected by adenosine and to focus on the cellular and subcellular mechanisms whereby adenosine regulates CBF. We will utilize in vivo and in vitro vessel preparations to study adenosine's integrated function in the cerebral arteriole, culture techniques to study the cellular physiology of adenosine, and electrophysiologic methods to define the mechanism of action of adenosine. In addition, in whole brain, we will analyze the role of adenosine in a pathophysiologic state hyperglycemic ischemia and reperfusion. Specific aims: 1) To test the hypothesis that attenuated adenosine concentrations in brain during hyperglycemic ischemia and reperfusion are casually related to the increase brain injury associated with hyperglycemic ischemia; 2) To test the hypothesis that diffusion, flow and/or conduction mechanism are involved in pial arteriolar vasodilation in sensory cortex during sciatic nerve stimulation; 3) Using cell culture techniques to define the metabolism of adenosine, we will test tht hypothesis that different cell types are capable of producing adenosine; 4) Using an in vitro vessl preparation, we will test the hypothesis that increased osmolarity causes vasodilation by the release of adenosine from cerebral microvascular endothelial cells; 5) Using electrophysiologic (whole cell and patch clamp) techniques, we will test the hypothesis that adenosine affects membrane and intracellular events. Further investigation of adenosine in brain will define the role of adenosine in metabolic regulation of CBF and allow a more rational treatment of stroke.